Ground eliminator system

ABSTRACT

Apparatus for use in an annunciator system wherein the system includes a plurality of remote sensors for detecting out-of-limit conditions and a central annunciator station with a plurality of alarm annunciator means for continuously monitoring the respective sensors and for giving an alarm indication in response to detection of an out-of-limit condition by the respective sensors, the sensors each being interconnected with the respective annunciator means by respective sensor leads which are subject to undesirable grounding. The apparatus includes means, constituted by relay circuitry, for detecting the grounding of an unidentified one of the sensor leads. A stepping switch constitutes means for scanning respective sensor leads for the presence of a grounded condition, and circuitry interconnected with the respective alarm annunciator means acts as a means operative during scanning for selectively causing any alarm annunciator means to indicate a grounded condition of its respective sensor lead.

United States Patent Kessler [15] 3,657,714 [451 Apr. 18,1972

GROUND ELIMINATOR SYSTEM Arthur R. Kessler, St Louis, Mo.

[73] Assignee: Electro Devices, Inc., St. Louis, Mo.

[22] Filed: June 10, 1970 [21] Appl. No.: 45,018

[ 72] Inventor:

3,087,144 4/ 1963 Bianchi et a1. ..340/413 Primary Examiner-David L. Trafton Attorney-Koenig, Senniger, Powers and Leavitt [57] ABSTRACT Apparatus for use in an annunciator system, wherein the system includes a plurality of remote sensors for detecting outof-limit conditions and a central annunciator station with a plurality of alarm annunciator means for continuously monitoring the respective sensors and for giving an alarm indication in response to detection of an out-of-limit condition by the respective sensors, the sensors each being interconnected with the respective annunciator means by respective sensor leads which are subject to undesirable grounding. The apparatus includes means, constituted by relay circuitry, for detecting the grounding of an unidentified one of the sensor leads. A stepping switch constitutes means for scanning respective sensor leads for the presence of a grounded condition, and circuitry interconnected with the respective alarm annunciator means acts as a means operative during scanning for selectively causing any alarm annunciator means to indicate a grounded condition of its respective sensor lead.

21 Claims, 3 Drawing Figures g Z/ 1 (/5 P1 1% P2 J; GROUND I S ANNUNCIATORS ELIMINATOR I 1 REMOTE ATTERY I SENSORS I SYSTEM I 5 ISOLATED GROUND POWER ALARM SUPPLY l GROUND ELIMINA'IOR SYSTEM BACKGROUND OF THE lNVENTlON The present invention relates to annunciator systems and more particularly to a system for use in annunciator systems which is operative todetect, identify, and eliminate grounds appearing on sensor leads interconnecting sensors of the an.- nunciator system with respective annunciators thereof.

In annunciator systems, it is common for there to be a plurality of remote sensors located at various stations as to which conditions are desired to be monitored by means of the sensors. These sensors areinterconnected by respective pairs of sensor leads with individual'alarrn annunciator means or socalled annunciators, all of which are located at a centralannunciator station. Typically, the sensors are constituted by either a normally open or normally closed switch operative in response to an out-of-limit condition. While sensor circuits of both open-circuit and closed-circuit types may be employed in a particular system, it is usual in any case that the sensors are supplied by a common power sourcesuch as a station battery. As will be understood, the sensor leads are subject to undesirable grounding, this grounded condition being due, for example, to an exposed sensor lead conductor coming into contact with a grounded object. Since'the sensor leads are connected through the respective annunciators in common across the station battery, such a grounded condition is undesirable since, if assuming the grounded sensor lead to be of one polarity, the subsequent grounding of a lead of the opposite polarity, e.g., a negative lead, may act either to .cause false operation of control equipment connected across the sta tion battery or to cause a direct short-circuit across the station battery thereby causing circuit breakers or other protective circuitry to operate to disconnect or isolate the station battery. Since either result may cripple the effectiveness of the annunciator system, it is highly desirable to detect, identify and eliminate the grounded condition'of a sensor lead. Since there may be many annunciator points in z particular annunciator system, this identification and elimination process must desirably be carried out quickly and without difiiculty.

Heretofore, it has been proposed to utilize an inverter, isolation transformer and a DC power supply between the station battery and the annunciator system in order to isolate the battery from the sensor leads. While this arrangement acts to protect the various circuits across the station battery from being disabled by a short-circuit, such an isolation technique requires expensive heavy-duty apparatus which still fails'to prevent a subsequent grounded condition from appearing as a short across the power leads to the annunciator system, thus possibly rendering the annunciator system inoperable (even through the station battery may itself be isolated). Furthermore, even when such an isolation arrangement is utilized, it is still necessary to manually search for the ground by disconnecting individual sensor leads or sets of sensor leads from the station battery. This is not only time consuming but disadvantageous in that it temporarily disables the annunciation function of annunciator points as to which the sensor leads have been disconnected.

BRIEF SUMMARY OF THE INVENTION Accordingly, among the several objects of the present invention may be noted the provision of apparatus for use in annunciator systems which will detect the grounding of unidentified sensor leads of the system; the provision of such apparatus which will scan the respective sensor leads for the presence of the grounded condition; the provision of such apparatus which, during scanning, will selectively cause any individual annunciator to indicate a grounded condition of its respective sensor lead; the provision of such apparatus which will automatically disconnect a grounded sensor lead, thereby preventing the threat of a short-circuit across the station battery because of any subsequent grounding of a sensor lead; the provision of such apparatus which utilizes the annunciation function of individual annunciators of the annunciator system cleared conditionythe provision of such apparatus which is reliable, long-lastingin operation andrelatively inexpensively constructed. Other objects and features will be in part ,apparent and in part pointed out hereinafter.

Briefly, ground-eliminating apparatus is described for use in annunciator systems having a plurality of remote sensors for detecting out-of-lirnit conditions and respective centrally located annunciator means for each of the sensors interconnected therewith by respective pairs of sensor leads subject to undesirable grounding. The annunciator means are each supplied by a common power source, i.e., a station battery, and each continuously monitors the respective sensor and is operative to give an alarm ir'i'dication in response to detection of an out-of-limit condition by its respective sensor. The apparatus includes ground-detecting means constituted by relay circuitry interconnected by leads with the power source. This means is responsive to voltages on the power source leads with respect to ground and serves to detect the grounding of an unidentified one of the sensor leads. Alarm means'is operative in response to detection by'the detecting means of a sensor lead grounded condition and gives alarm indication of the existence of the grounded condition. Scanning means comprising a stepping switch is operative in response to the detection by the detecting means of a sensor leadgrounded condition. The stepping switch scans respective pairs of sensor leads for the presence of the grounded condition and momentarily opens the respective pairs of sensor leads as the pairs are scanned. Circuitry interconnected with the stepping switch constitutes means responsive to a grounded condition of any of the sensor leads for immediately tenninating the scanning at a pair of sensor leads one of which has a grounded condition. This thelast-said pair of sensor leads are opened and thereby disconnected from the common power source. Finally, circuit-means is provided which is responsive to the scanning for causing indication by the respective alarm annunciator'means as each pair of sensor leads is scanned. In this way, when scanning is terminated at a pair of sensor leads one of which has a grounded condition, the last-said pair of sensor leads is identified by the respective alarm annunciator means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a ground eliminator system of the invention used with an annunciator system;

FIG. 2 is a schematic circuit diagram of a ground eliminator system of the invention and relevant connected portions of the annunciator system with which it is used; and

FIG. 3 is a schematic circuit diagram of an individual annunciator of the system of FIG. 2.

Corresponding reference characters indicate corresponding parts throughout the views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a ground eliminator system of the present invention is shown interconnected with an annunciator system having a plurality of remote sensors S1, S2, Sn and a central annunciator station 11 having respective alarm annunciator means for each of the sensors. As is common practice, the several annunciators are supplied by a common power source constituted by a so-called station battery 13 connected by a pair of leads L1 and L2. A battery, rather than a conventional AC. power supply, is used to ensure operation if conventional AC power sources should be rendered inoperative.

As is understood by those skilled in the art, the sensors S1-Sn are constituted by sensing contacts which are either normally open or normally closed. The several remote sensors may monitor various conditions such as temperature, pressure, position, or other conditions. For this purpose, the sensing contacts of each sensor are interconnected with the respective annunciator at the central annunciator station 11 by pairs of sensor leads, these pairs being represented in FIG. 1 as single leads designated P1, P2 Pn. When there is an out-of-limit condition such as an abnormal pressure, etc., operation of the sensing contacts of a sensor causes out-of- ,limit alarm indication at the respective annunciator associated with that sensor.

The detailed circuitry of the respective annunciators is described in detail hereinbelow. For the present, however, it is sutficient to note that the annunciator station 11 generally comprises a panel arrangement wherein the respective annunciators each include an indicator panel providing colored or flashing light indication. These indicator panels are arranged in suitable manner for being observed by supervisory personnel at a control facility. In any case, the voltage across each of the sensor leads Pl-Pn is supplied by the common power source constituted by the station battery 13.

As noted previously, individual ones of the pairs of sensor leads are subject to becoming grounded, for example, where the insulation on one of the leads is broken and the lead then contacts a grounded object. Since the station battery acts as a power source common to all of the sensor leads, the grounded condition of one of the sensor leads is undesirable since it .presents a possibility of a short-circuit across the station battery should another sensing'lead become grounded, resulting in operation of conventional protective circuitry (not shown) which disconnects the battery from the annunciator system.

A ground eliminator system of the invention is designated 15 and is shown interconnected in the pairsof sensor leads Pl-Pn. The ground eliminator system functions, first, to de-' tect a grounded sensor lead; second, to locate and disconnect the grounded lead; and, third, to announce or identify the cation of the grounded lead to an observer. Preferably alarm means 17 is utilized as a part of the ground eliminator system for giving alarm indication of the existence of the grounded condition. A power supply 19 which provides isolation from the AC power source and which is independent of the station battery is also a part of the ground eliminator system.

Referring now to FIG. 2, the individual annunciators are designated A1, A2, An and are connected in parallel across the power leads L1 and L2 from the station battery 13. The annunciators are here shown as being of the type wherein a first color such as white is displayed by a lamp X1 to give an out-of-limit alarm indication signalling a sensor alarm occurrence, a second color such as red is displayed by a second lamp X2 signalling an alarm pending condition, and a third color such as green is displayed by a third lamp X3 signalling an alarm cleared condition. The pairs of leads Pl-Pn are interconnected with the sensing contacts, designated SCl, SC2, 501, of the remote sensors S1, S2, Sn. While the sensor leads of a pair are-typically individually referred to in the art as 5" and C" leads, in order to avoid confusion herein these leads will be referred to hereinafter as the a and b leads,

respective one of the contacts of set B2, these latter'contacts also being successively momentarily opened by a wiper B2W upon stepping action. v

A further set of normally open contacts which are adapted to be momentarily contacted by a wiper B3W is designated B3. These contacts of set B3 are connected to the respective a sensor leads on the sensor side of the contacts BlW. A similar set of contacts is designated B4. These latter contacts are also normally open and are adapted to be momentarily contacted by a wiper B4W. The contacts of set B4 are connected to the b sensor leads on the sensor side of the contacts of setB. A fifth set of contacts is designated B5. Contacts of this set are also normally open and are adapted to be momentarily contacted by a wiper BSW. The latter contacts are connected to the respective a sensor leads between the set B1 and the annunciators Al-An. The connections from each of the wipers B3W-B5W are described hereinbelow.

Connected across the battery leads L1 andL2 is a ground detecting relay or so-called differential or balanced relay indicated generally at 23. Relay 23 acts as a means for'detecting the grounding of an unidentified oneof the sensor leads, as

will become apparent, and includes a pair of windings 23W respectively. Accordingly, the leads of the pair ,P1 are designated. Fla and Plb, the leads of the pair P2 are designated P2a and P2b, and the leads of the pair-Pn are designated Pna and Pub. i 7

Each of the a leads is connected through the normally closed contacts of a first set or level of so-called bank contacts of a five-level stepping switch. This first set of contacts is designated generally B1 and includes a normally closed pair of contacts for each of the a leads. The individual contacts are not designated to avoid confusion. As those skilled in theart understand, the contacts are adapted to be successively momentarily opened by a wiper BlW which is advanced in steplike movements by a motor magnet 21 of the stepping switch. A second set of normally closed bank contacts is and 23W in series across the leads L1 and L2 with their common connection point being connected to ground. windings 23W and 23W are connected with'opposite magnetic polarity as indicated to cause a normally open pair of contacts 23 to close when there is an imbalance on either of lines L1 and L2 with respect to ground, such as would occur upon the grounding of a sensor lead. As will be seen, contacts 23K when closed are adapted to cause energization of motor magnet 21. For this purpose, a connection is made from lead Ll through contacts 23K and then through a cutotf switch 25 (which permits the ground eliminator system to be disabled of desired) and then through the normally closed contacts 271(1 and 29K! of a respective pair of relays indicated generally at 27 and 29. Relays 27 and 29 are part of circuitry which acts as means for terminating scanning by the stepping switch for sensor leads having a grounded conditionwhenever the grounded sensor lead is contacted. The connection then continuesfrom contacts 291(1 via a lead 31 through the normally closed contact 331(1 of a pacer relay indicated generally at 33, thence to motor magnet 21 The return lead 35 for motor magnet 21 is connected to the negative side of the station battery 13, as indicated by the temtinal having a negative sign. Similar connections to the station battery negative tenninal and to the positive terminal are indicated similarly elsewhere in H6. 2.

The stepping switch includes a pair of interrupter contacts 37 which are adapted to .close momentarily each time the wipers of the stepping switch are advanced one step. Operation of the stepping switch is such that the wipers are advanced one step each time motor magnet 21 is deenergized. Contacts 37 are connected in a circuit from lead 31, through an adjustable resistor R1, through the winding 33W of, pace relay 33, thence to the negative terminal of the station battery. A capacitor C1 is is connected across relay winding 33W and with resistor R1 provides an RC pacer network regulating the rise time of current in relay winding 33W. Accordingly, as the motor magnet 21 causes steplike movements'of the wipers, contacts 37 are respectively momentarily closed, each closure thereof energizing relay winding 33W to cause momentary opening of contacts 33Kl. This has the efiect of causing the stepping switch to operate at a steady rate such as 10 steps per second, depending upon the setting of resistor R1. Pacer relay 33 also has a second set of normally closed contacts 3310 which complete a circuit from the positive terminal of the station battery to wiper BSW of the stepping switch.

When contacts 23K close, the connection is also made from lead Ll of the station battery through switch 25 to alarm 17 by means of a lead 37, the othersideof the alarm being connected to the negativeterminalof the station battery as indicated. Alarm 17, which may, forexample, be constituted by designated B2. Each of the b leads is connected through a has the purpose of giving a separate ground alarm indication of the existence of a grounded condition and is operative in response to the detection by the ground detector relay 23 of a sensor lead grounded condition.

The stepping switch includes yet another pair of contacts 39 which are nonnally open when wipers BlW-BSW are in their home positions but which close whenever the wipers are being advanced in stepwise movements. When closed, contacts 39 complete a circuit from the positive side of the station battery through an isolation diode D1 and thus act to keep alarm 17 energized as long as the stepping switch is operating (i.e., when the wipers are out of home position) even though contacts 23K of ground detector relay 23 may have opened during the interim. It will be also seen that even though the opening of contacts 23K may have occurred, a connection is also maintained from the positive side of the station battery through contacts 39 by means of lead 37, thus to continue providing voltage for energizing motor magnet 21. A normallyv open pushbutton or so-called scan advance switch P81 is connected between motor magnet 21 and the positive terminal of the station battery for selectively causing resumption of scanning after scanning has been terminated.

As noted previously, this termination of scanning is efl'ected by relays 27 and 29. For this purpose, these relays have respective windings 27W and 29W which are supplied by AC power at a suitable voltage, e.g., 24 volts, by means of a power supply 19 which may, for example, comprise a stepdown isolation transformer to which AC line voltage is supplied by a pair of input leads L3 and L4. One of the output leads of power supply 19 is identified at 41 and is connected to one side of each of windings 27W and 29W. The other side of each of these windings is connected to a respective one of wipers B3W and B4W. Each of relays 27 and 29 includes a further respective set of normally open contacts 27K2 and 29I(2 each of which is connected in a respective circuit be means of a lead 43 between the positive and negative terminals of the station battery including a respective light bulb Xa and Xb. As will be seen, bulb Xa indicates that an a sensor lead has been grounded and bulb Xb that a b sensor lead has been grounded.

The other lead from power supply 19 is designated 45 and is connected through the normally closed contacts 47Kl of a relay 47, thence to ground. As will be seen, relay 47 is part of selectively operable ground test circuitry operable to test whether the ground eliminator system is operating properly and constitutes means for interposing a predetermined impedance between a preselected sensor lead and ground to simulate a grounded condition of the preselected sensor lead. For this purpose, winding 47W of relay 47 is connected through a normally open ground test pushbutton PB2 to the positive terminal of the station battery, the other side of this winding being connected to the negative terminal of the station battery. Whenever pushbutton PB2 is closed to energize winding 47W, contacts 47K] are opened and a second set of contacts 47Kl are closed to connect lead 45 from power supply 19 to a lead 49 connected commonly to one end of each of a pair of resistors R2 and R3. The other ends of each of these resistors are respectively connected to the corresponding a and b leads of a preselected pair of sensor leads. While, for the purpose of determining whether or not the system 5 performing satisfactorily, this pair may be any arbitrarily preselected pair, resistors R2 and R3 are here shown connected to the respective a and b leads of the pair Pn on the sensor side of contact sets B1 and B2 respectively. Relay 47 also includes second and third sets, designated 47K2 and 47K3, of normally open contacts which are adapted to close upon energization of winding 47W. When closed, contacts 47K2 set up a holding circuit for relay winding 47W or relay 47 by means of a lead 51 connected from one of contacts 47K2 to the anode of diode D1. When closed, contacts 47KB provide a connection from a positive terminal of the station battery to lead 37 for supplying power via contacts 271(1 and 291(1 for energization of motor magnet 21.

Referring to FIG. 3, there is illustrated the circuitry of individual alarm annunciator A1 of FIG. 2. Connections to the positive and negative terminals of station battery 13 via leads L1 and L2 are so designated. Sensor leads Pla and Plb are also designated to correspond with FIG. 2. Closing of sensor contacts SCl, which are represented by dashed lines in FIG. 3, completes a circuit from the positive terminal of the station battery through a diode D2 across the red lamp X2. At the same time, the battery voltage is supplied to a pulse-forming circuit constituted by resistors R4-R8, and capacitors C2-C5.

This pulse-forming circuit supplies a pulse through resistor R6 to the gate electrode of a silicon controlled rectifier (SCR), designated SCRl, whose cathode and anode terminals are connected in a circuit including diodes D3 and D4 and the white lamp Xl between the cathode of diode D2 and the negative side of the station battery. This SCR is accordingly triggered and conducts to illuminate white lamp X2, signalling a sensor alarm occurrence, i.e., an out-of-limit condition, and also green lamp X3, which is connected between the station battery positive terminal and the anode of SCRI.

Though all three lamps X1, X2 and X3 are then illuminated behind the usual annunciator panel, white lamp X1 is brighter than the other two and prevails. Thus only a white signal appears to be given.

Triggering SCR! energizes, via a diode D5, an annunciator alarm 53, which may comprise a buuer or the like, providing an aural warning. Triggering of SCRI also causes a capacitor C6 to charge a potential determined by a voltage divider constituted by a pair of resistors R9 and R10. To acknowledge the lamp and aural indications of sensor alarm occurrence, an operator may depress a normally open acknowledge pushbutton PB3, one side of which is connected to the negative terminal of the station battery and the other side of which is connected through a diode D6 between resistors R9 and R10. Pushbutton PB3 is connected via a bus to each of the individual annunciators, as the dashed line connection serves to illustrate.

The momentary closing of pushbutton PB3 discharges capacitor C6 across SCRl to commutate and thus render this SCR nonconductive. Lamps X1 (white) and X3 (green) are thereby extinguished. However, lamp X2 remains energized, providing a red panel indication which signals an alarm pending condition.

While the sensor contact SC] are closed, a capacitor C9 is charged. When there is no longer an out-of-Iimit condition, contacts SCl open. One side of capacitor C9 is connected between a pair of resistors connected between the positive side of the station battery and the cathode of diode D3. The other side of capacitor C9 is connected to the cathode of SCRI. The resistance ratio of resistors R11 and R12 is such that, when sensor contacts SCl open, capacitor C9 discharges to temporarily make the cathode of SCRl negative with respect to its gate electrode, triggering the SCR. This energizes green lamp X3, but white lamp X1 is not illuminated because sensing contacts SCl have opened. This green indication ordinarily signals an alarm cleared condition. To extinguish green lamp X3, the operator again depresses pushbutton PB3 and the charge on capacitor thereby commutates SCRl. The annunciator is thus in a quiescent or reset condition.

Testing of this annunciator may be accomplished by depressing a normally open pushbutton P84 which connects the positive terminal of the station battery to each annunciator A1-An via a bus. If operation is proper, SCRl is triggered causing lamp illumination. Resetting is then accomplished by depressing pushbutton PB3 as described above.

In operation of the ground eliminator system, it is assumed that switch 25 is closed and that initially there are no grounded sensor leads. Ordinary operation of the annunciator system is such that if one of the sensors Sl-Sn detects an outof-Iimit condition, the respective sensor contact SCI-SCn either opens or closes, and this is indicated at the respective annunciator Al-An. Thus, if sensor contacts SCI close, bulb X1 will give a white indication to signal a sensor alarm occurrence. In other types of annunciator systems there may be a flashing light indication at the annunciator. Such ordinary alarm signalling has no eflect on the ground eliminator system.

Should one of the sensor leads become grounded, there will be an unbalanced condition of the leads L1 and L2 from the station battery with respect to ground. Thus assuming an a sensor lead is grounded, lead L1 will drop essentially to ground potential and the resultant imbalance of potential across windings 23W and 23W will close contacts 23K. Accordingly, the positive side of station battery 13 is connected through contacts 23K, lead 43, relay contacts 271(1 and 29Kl, lead 31, thence through relay contacts 33K1 to motor magnet 21 of the stepping switch. Alarm 17 is simultaneously energized via lead 37.

Energization of motor magnet 21 causes stepping action of wipers BlW-BSW. Wipers BlW and B2W act to momentarily open the respective a and b sensor leads as the wipers are successively advanced. Wipers BSW and B4W act to successively connect the lower side of the relay windings 27W and 29W to the a sensor leads Tla-Tna and the b sensor leads Tlb-Tnb, respectively. Thus the stepping switch acts as a scanning means operative in response to the detection by the ground detector relay 23 of a sensor lead grounded condition for scanning respective pairs of the sensor leads for the presence of the grounded condition. If either wiper B3W or B4W con tacts an a or b sensor lead which is grounded, the respective relay winding 27W or 29W is energized by power supply 19 because of the path to ground provided by the grounded lead. Relay contacts 27K1 or 291(1 are opened by the energization of the respective winding 27W or 29W. Since the energizing circuit for motor magnet 21 is completed through these contacts, the opening of either of contacts 27K1 or 29K1 will cause scanning to immediately be terminated, i.e., will stop the stepping switch at the position in which the wiper B3W or B4W contacts the grounded sensor lead. Since wipers BlW and 82W act to break the a and b sensor leads, respectively, the sensor leads of the pair at which the stepping switch has been stopped are disconnected. Thus it may be seen that relays 27 and 29 and power supply 19 which provides power therefor together constitute a means for immediately terminating scanning at a pair of sensor leads, one of which has a grounded condition.

The location of the annunciator point as to which there is a grounded sensor lead is determined by referring to the annunciators Al-An. The interconnections of the contact of set B with the individual sensor leads of the pairs Pl-Pn together with contacts 33K2 interconnected with wiper BSW provide means responsive to scanning by the stepping switch for selectively causing alarm indication by each of the annunciators Al-An as the respective sensor leads are scanned thereby to indicate a grounded condition of a respective sensor lead. As wiper BSW contacts each of the a sensor leads as the wipers are advanced in stepwise movements, a positive potential is supplied from the station battery having the efiect of causing each of the enunciators to give an alarm indication. As noted, contacts 331(2 are also momentarily opened once during each stepping movement of the wipers. Hence, those annunciators adapted to respond to an open sensor circuit are also caused to give alarm indication.

In the three-color annunciator system described herein, this momentary contacting of the a sensor leads by the positive battery potential (or else opening of the sensor circuit), has

' the efiect not only of causing the respective annunciators to signal an alarm indication by transitorily displaying the first color white, as the momentary contacting or opening of sensor circuit takes place but also to display a third color, green, signalling an alarm cleared condition, after the respective sensor lead is scanned. Thus when scanning is terminated, the pair of sensor leads (one of which is grounded) is identified by the annunciator displaying white as an alarm indication. Previously scanned sensor leads are then identified by annunciators which display green, ordinarily signalling an alarm cleared condition. 1

Whether relay winding 27W or relay winding 29W is energized depends upon whether an a or a b sensor lead is grounded. Since wiper 83W contacts a sensor leads, the grounding of one of these causes contacts 27K2 of relay 27 to close, illuminating bulb Xa. Similarly, the grounding of a b sensor lead efl'ects operation of relay 29 and closes contacts 29K2 to illuminate bulb Xb.

From the foregoing, it may be seen that the ground eliminator system acts automatically not only to announce the indication of a sensor lead grounded condition, but also automatically scans for the location or identity of the pair of sensor leads as to which one is grounded and automatically disconnects that pair of sensor leads. The identity of that pair of sensor leads is then indicated on the annunciator panels by color. Further, the particular one of the sensor leads is identified by energization of either the bulb Xa or Xb, signalling whether it is the a or b sensor lead of that pair which is grounded.

A control-room operator or other person monitoring the operation of the annunciator system will be alerted by energization of alarm 17 to the existance of a grounded condition. The annunciators indicate and thus identify the sensor point as to which there is a grounded condition. That annunciator may then be disconnected, e.g., by pulling the'annunciator circuit board or appropriate components from the annunciator panel. Repairs may then be effected to eliminate the grounded condition while the remainder of the annunciator system continues to operate normally. l-laving disconnected the faulty annundam and its sensor leads, the operator may then depress pushbutton PHI to cause resumption of scanning. This reenergizes motor magnet 21 and the stepping switch accordingly proceeds to scan the remainder of sensor leads for an remaining rounds, If there are such, the grounded leads are identified in the above manner and the appropriate annunciator or annunciators may then be disconnected. Assuming there are no further grounds, the stepping switch wipers BlW-BSW return to the home position (as shown) whereupon contacts 39 open to stop the stepping switch operation so that the system is then once more ready for normal operation.

The ground test circuitry of the invention operates as follows: Since it is desired that the system have a predetermined sensitivity, i.e., that it indicate a grounded condition whenever the resistance between any sensor lead and ground drops below a predetermined value, the test resistors R2 and R3 are preselected of a value substantially equal to this minimum sensitivity. To test operation of the ground eliminator system, pushbutton P82 is depressed, energizing relay winding 47W. This closes contact 47Kl', shifting lead 45 from power supply 19 from ground and connecting it instead to one side of each of the commonly connected resistors R2 and R3. As noted previously, resistors R2 and R3 are connected to a preselected pair of sensor leads and represent a predetennined impedance between those preselected sensor leads and ground simulating a grounded condition of the preselected sensor leads. Energization of relay winding 47W also closes contacts 47K2 and 47KB. The latter energizes motor magnet 21 and thus initiates scanning of the sensor leads for the presence of a grounded condition.

If operation of the system is normal, when wipers B3W and MW contact sensor leads to which resistors R2 and R3 are connected, scanning will terminate at this pair of sensor leads. The identity of the sensor leads will then be indicated by means of the color indications of the proper annunciator (annunciator An for the system shown in FIG. 2). Accordingly, the preselected pair of sensor leads to which resistors R2 and R3 have been connected will be correctly identified. Contacts 47K2 act to complete a holding circuit for relay winding 47W so that scanning will continue, even though pushbutton P82 is released, until the preselected sensor leads have been correctly identified as having a grounded condition or else'the wipers return to home position. When scanning has terminated at the correct sensor leads, scanning may then be resumed by depressing scan advance pushbutton P81 and operation of the stepping switch will then cause wipers BlW-BSW to return to home position.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an annunciator system having a plurality of remote sensors for detecting out-of-limint conditions and a central annunciator station with a plurality of alarm annunciator means for continuously monitoring the respective sensors and for giving an out-of-limit alarm indication in response to detection of an out-of-limit condition by the respective sensors, the sensors each being interconnected with the respective annunciator means by respective sensor leads which are subject to undesirable grounding, apparatus comprising:

means for detecting the grounding of an unidentified one of the sensor leads;

means for scanning respective sensor leads for the presence of a grounded condition; and

means operative during scanning for selectively causing any alarm annunciator means to indicate a grounded condition of its respective sensor lead.

2. In an annunciator system as set forth in claim 1, said apparatus further comprising alarm means operative in response to detection by the ground-detecting means of the grounding of a sensor lead for giving alarm indication of the existence of the grounded condition.

3. In an annunciator system as set forth in claim 1, said means for causing any annunciator means to indicate a grounded condition being operative to cause any annunciator means having a respective grounded sensor lead to give said out-of-limit alarm indication.

4. In an annunciator system as set forth in claim 1, means responsive to said ground-detecting means for actuating said scanning means to initiate scanning of the respective sensor leads upon the occurrence of the grounding of an unidentified sensor lead.

5. In an annunciator system as set forth in claim 1, said apparatus further comprising means interconnected with the scanning means and responsive to the sensing of a grounded sensor lead for immediately terminating said scanning at the grounded sensor lead.

6. In an annunciator system as set forth in claim 5, said scanning means being operative to momentarily open a respective sensor lead as the sensor leads are scanned whereby when scanning is terminated at a sensor lead having a grounded condition, the grounded sensor lead is opened and thereby is disconnected.

7. In an annunciator system as set forth in claim 6, said apparatus further comprising manually actuable scan advance means for causing resumption of said scanning after scanning has been terminated.

8. In an annunciator system as set forth in claim 6, said scanning means comprising an electrically energizable stepping switch including a motor magnet energized by said ground-detecting means for stepping action in response to the detection of a sensor lead grounded condition, said stepping switch having at least one level of normally closed contacts through which respective ones of the sensor leads are connected, the normally closed contacts each momentarily being opened by a wiper therefor during stepping action, and having at least one further level of normally open contacts and a further wiper therefor, the normally open contacts being connected to respective ones of the sensor leads between the respective normally closed contacts and the respective remote sensors, said further wiper being interconnected with the means for terminating scanning.

9. In an annunciator system as set forth in claim 6, said system including a common power source supplying each of the alarm annunciator means said ground-detecting means comprising a difierential relay connected across leads from the common power source and having a pair of contacts of an unbalanced condition on the power source leads with respect to ground.

10. In an annunciator system as set forth in claim 9, the means for terminating scanning comprising a further power source one side of which is grounded, the further power source being independent of said common power source, and relay means including normally closed relay contacts interconnected between said ground-detecting means and the motor magnet of said stepping switch, said relay means being interconnected between said further-power source and said further wiper of the stepping switch whereby the normally closed relay contacts are opened to prevent further energization of the motor magnet of said stepping switch thereby to terminate stepping action when said further wiper contacts one of the sensor leads having a grounded condition.

11. In an annunciator system as set forth in claim 1, selectively operable ground test circuitry-comprising means for interposing a predetermined impedance between a preselected sensor lead and ground to simulate a grounded condition of the preselected sensor lead.

12. An annunciator system comprising:

a plurality of remote sensors for detecting out-of-limit conditions;

a central annunciator station with a plurality of alarm annunciator means interconnected to respective sensors by respective sensor leads, said sensor leads being subject to undesirable grounding, each annunciator means continuously monitoring its respective sensor and operative to give an alarm indication in response to detection of an out-of-limit condition by its respective sensor, the respective annunciator means each displaying a first color signalling sensor alarm operation, a second color signalling an alarm pending condition, and a third color signalling an alarm cleared condition;

a common power source for said annunciator means;

means for detecting the grounding of an unidentified one of the sensor leads;

means for scanning respective sensor leads for the presence of a grounded condition; and means operative during scanning for causing the annunciator means to display at least one of said colors as an indication that a respective sensor lead thereof is grounded.

13. An annunciator system as set forth in claim 12 further comprising means interconnected with the scanning means and responsive to the grounded condition of any of the sensor leads for immediately terminating scanning at a sensor lead having a grounded condition, wherein the means for causing the annunciator means to display at least one of said colors is operative to cause the respective annunciator means to transitorily display said first color as the respective sensor lead is scanned and to display said third color after the respective sensor lead is scanned whereby, when scanning is terminated at a sensor lead having a grounded condition, the last-said sensor lead is identified by display of said first color and previously scanned sensor leads are identified by display of said third color.

14. An annunciator system as set forth in claim 13 wherein said scanning means is operative to momentarily open respective sensor leads as the sensor leads are scanned whereby when scanning is terminated at a sensor lead having a grounded condition, the grounded sensor lead is opened and thereby ia disconnected.

15. In an annunciator system as set forth in claim 14 said scanning means comprising an electrically energizable stepping switch including a first set of contacts for momentarily opening respective sensor leads during stepping action, a further set of contacts for momentarily connecting the means for terminating scanning to respective sensor leads during stepping action, and a still further set of contacts for momentarily connecting the means for causing said first color indication to each of the respective annunciator means during adapted to energize said stepping switch upon the occurrence stepping action.

16. An annunciator system as set forth in claim 12 wherein said apparatus further comprises means responsive to said ground-detecting means for actuating said scanning means to initiate scanning of the respective sensor leads upon the occurrence of the grounding of an unidentified sensor lead.

17. Ground-eliminating apparatus for use in annunciator systems having a plurality of remote sensors for detecting outof-limit conditions and respective centrally located annunciator means for each of the sensors interconnected therewith by respective pairs of sensor leads subject to undesirable grounding, the annunciator means each being supplied by a common power source and each continuously monitoring the respective sensor and being operative to give an alarm indication in response to detection of an out-of-lirnit condition by its respective sensor, said apparatus comprising:

ground-detecting means interconnected by leads with the power source and responsive to voltages on the power source and responsive to voltages on the power source leads with respect to ground for detecting the grounding of an unidentified one of the sensor leads;

alarm means operative in response to detection by the detecting means of a sensor lead grounded condition for giving alarm indication of the existence of the grounded condition; scanning means also operative in response to the detection by the detecting means of a sensor lead grounded condition for scanning respective pairs of sensor leads for the presence of the grounded condition, said scanning means momentarily opening the respective pairs of sensor leads as said pairs are scanned;

means interconnected with the scanning means responsive to a grounded condition of any of the sensor leads for immediately terminating said scanning at a pair of sensor leads one of which has a grounded condition whereby the last-said pair of sensor leads are opened and thereby disconnected from the common power source; and

means responsive to said scanning for causing indication by the respective alarm annunciator means as each pair of sensor leads is scanned whereby, when scanning is terminated at a pair of sensor leads one of which has a grounded condition, the last-said pair of sensor leads is identified by the respective alarm annunciator means.

18. Ground-eliminating apparatus as set forth in claim 17 wherein said scanning means comprises an electrically energizable stepping switch including sets of contacts interconnected with said pairs of sensor leads, a motor magnet and wipers for said sets operated by said motor magnet, at least one of said wipers being interconnected with means for terminating scanning.

19. Ground-eliminating apparatus as set forth in claim 18 wherein the means for tenninating scanning includes relay means having contacts interconnected with said motor magnet.

20. Ground-eliminating apparatus as set forth in claim 19 wherein said relay means includes a first and second relay each including an energizing winding interconnectedwith a respective one of said wipers, said relays having respective contacts connected for energizing respective indicator means for signalling which sensor lead of a pair of sensor leads is grounded.

21. Ground-eliminating apparatus as set forth in claim 17 further comprising manually actuatable scan advance means for causing resumption of said scanning after scanning has been terminated. 

1. In an annunciator system having a plurality of remote sensors for detecting out-of-limit conditions and a central annunciator station with a plurality of alarm annunciator means for continuously monitoring the respective sensors and for giving an out-of-limit alarm indication in response to detection of an outof-limit condition by the respective sensors, the sensors each being interconnected with the respective annunciator means by respective sensor leads which are subject to undesirable grounding, apparatus comprising: means for detecting the grounding of an unidentified one of the sensor leads; means for scanning respective sensor leads for the presence of a grounded condition; and means operative during scanning for selectively causing any alarm annunciator means to indicate a grounded condition of its respective sensor lead.
 2. In an annunciator system as set forth in claim 1, said apparatus further comprising alarm means operative in response to detection by the ground-detecting means of the grounding of a sensor lead for giving alarm indication of the existence of the grounded condition.
 3. In an annunciator system as set forth in claim 1, said means for causing any annunciator means to indicate a grounded condition being operative to cause any annunciator means having a respective grounded sensor lead to give said out-of-limit alarm indication.
 4. In an annunciator system as set forth in claim 1, means responsive to said ground-detecting means for actuating said scanning means to initiate scanning of the respective sensor leads upon the occurrence of the grounding of an unidentified sensor lead.
 5. In an annunciator system as set forth in claim 1, said apparatus further comprising means interconnected with the scanning means and responsive to the sensing of a grounded sensor lead for immediately terminating said scanning at the grounded sensor lead.
 6. In an annunciator system as set forth in claim 5, said scanning means being operative to momentarily open a respective sensor lead as the sensor leads are scanned whereby when scanning is terminated at a sensor lead having a grounded condition, the grounded sensor lead is opened and thereby is disconnected.
 7. In an annunciator system as set forth in claim 6, said apparatus further comprising manually actuable scan advance means for causing resumption of said scanning after scanning has been terminated.
 8. In an annunciator system as set forth in claim 6, said scanning means comprising an electrically energizable stepping switch including a motor magnet energized by said ground-detecting means for stepping action in response to the detection of a sensor lead grounded condition, said stepping switch having at least one level of normally closed contacts through which respective ones of the sensor leads are connected, the normally closed contacts each momentarily being opened by a wiper therefor during stepping action, and having at least one further level of normally open contacts and a further wiper therefor, the normally open contacts being connected to respective ones of the sensor leads between the respective normally closed contacts and the respective remote sensors, said further wiper being interconnected with the means for terminating scanning.
 9. In an annunciator system as set forth in claim 6, said system including a common power source supplying each of the alarm annunciator means said ground-detecting means comprising a differential relay connected across leads from the common power source and having a pair of contacts adapted to energize said stepping switch upon the occurrence of an unbalanced condition on the power source leads with respect to ground.
 10. In an annunciator system as set forth in claim 9, the means for terminating scanning comprising a further power source one side of which is grounded, the further power source being independent of said common power source, and relay means including normally closed relay contacts interconnected between said ground-detecting means and the motor magnet of said stepping switch, said relay means being interconnected between said further power source and said further wiper of the stepping switch whereby the normally closed relay contacts are opened to prevent further energization of the motor magnet of said stepping switch thereby to terminate stepping action when said further wiper contacts one of the sensor leads having a grounded condition.
 11. In an annunciator system as set forth in claim 1, selectively operable ground test circuitry comprising means for interposing a predetermined impedance between a preselected sensor lead and ground to simulate a grounded condition of the preselected sensor lead.
 12. An annunciator system comprising: a plurality of remote sensors for detecting out-of-limit conditions; a central annunciator station with a plurality of alarm annunciator means interconnected to respective sensors by respective sensor leads, said sensor leads being subject to undesirable grounding, each annunciator means continuously monitoring its respective sensor and operative to give an alarm indication in response to detection of an out-of-limit condition by its respective sensor, the respective annunciator means each displaying a first color signalling sensor alarm operation, a second color signalling an alarm pending condition, and a third color signalling an alarm cleared condition; a common power source for said annunciator means; means for detecting the grounding of an unidentified one of the sensor leads; means for scanning respective sensor leads for the presence of a grounded condition; and means operative during scanning for causing the annunciator means to display at least one of said colors as an indication that a respective sensor lead thereof is grounded.
 13. An annunciator system as set forth in claim 12 further comprising means interconnected with the scanning means and responsive to the grounded condition of any of the sensor leads for immediately terminating scanning at a sensor lead having a grounded condition, wherein the means for causing the annunciator means to display at least one of said colors is operative to cause the respective annunciator means to transitorily display said first color as the respective sensor lead is scanned and to display said third color after the respective sensor lead is scanned whereby, when scanning is terminated at a sensor lead having a grounded condition, the last-said sensor lead is identified by display of said first color and previously scanned sensor leads are identified by display of said third color.
 14. An annunciator system as set forth in claim 13 wherein said scanning means is operatIve to momentarily open respective sensor leads as the sensor leads are scanned whereby when scanning is terminated at a sensor lead having a grounded condition, the grounded sensor lead is opened and thereby is disconnected.
 15. In an annunciator system as set forth in claim 14 said scanning means comprising an electrically energizable stepping switch including a first set of contacts for momentarily opening respective sensor leads during stepping action, a further set of contacts for momentarily connecting the means for terminating scanning to respective sensor leads during stepping action, and a still further set of contacts for momentarily connecting the means for causing said first color indication to each of the respective annunciator means during stepping action.
 16. An annunciator system as set forth in claim 12 wherein said apparatus further comprises means responsive to said ground-detecting means for actuating said scanning means to initiate scanning of the respective sensor leads upon the occurrence of the grounding of an unidentified sensor lead.
 17. Ground-eliminating apparatus for use in annunciator systems having a plurality of remote sensors for detecting out-of-limit conditions and respective centrally located annunciator means for each of the sensors interconnected therewith by respective pairs of sensor leads subject to undesirable grounding, the annunciator means each being supplied by a common power source and each continuously monitoring the respective sensor and being operative to give an alarm indication in response to detection of an out-of-limit condition by its respective sensor, said apparatus comprising: ground-detecting means interconnected by leads with the power source and responsive to voltages on the power source and responsive to voltages on the power source leads with respect to ground for detecting the grounding of an unidentified one of the sensor leads; alarm means operative in response to detection by the detecting means of a sensor lead grounded condition for giving alarm indication of the existence of the grounded condition; scanning means also operative in response to the detection by the detecting means of a sensor lead grounded condition for scanning respective pairs of sensor leads for the presence of the grounded condition, said scanning means momentarily opening the respective pairs of sensor leads as said pairs are scanned; means interconnected with the scanning means responsive to a grounded condition of any of the sensor leads for immediately terminating said scanning at a pair of sensor leads one of which has a grounded condition whereby the last-said pair of sensor leads are opened and thereby disconnected from the common power source; and means responsive to said scanning for causing indication by the respective alarm annunciator means as each pair of sensor leads is scanned whereby, when scanning is terminated at a pair of sensor leads one of which has a grounded condition, the last-said pair of sensor leads is identified by the respective alarm annunciator means.
 18. Ground-eliminating apparatus as set forth in claim 17 wherein said scanning means comprises an electrically energizable stepping switch including sets of contacts interconnected with said pairs of sensor leads, a motor magnet and wipers for said sets operated by said motor magnet, at least one of said wipers being interconnected with means for terminating scanning.
 19. Ground-eliminating apparatus as set forth in claim 18 wherein the means for terminating scanning includes relay means having contacts interconnected with said motor magnet.
 20. Ground-eliminating apparatus as set forth in claim 19 wherein said relay means includes a first and second relay each including an energizing winding interconnected with a respective one of said wipers, said relays having respective contacts connected for energizing respective indicator means for signalling which sensor lead of a pair of sensor leads is grounded.
 21. Ground-eliMinating apparatus as set forth in claim 17 further comprising manually actuatable scan advance means for causing resumption of said scanning after scanning has been terminated. 